Why Do NASA Launch Times Depend On Lighting Conditions?

The International Space Station photographed from Space Shuttle Discovery in March 2009. (NASA)

From The Air & Space Smithsonian:

It's all about the solar beta angle.

While it was a hydrogen leak on the pad that forced NASA to scrub the launch of space shuttle mission STS-127 on June 17, one main reason the agency had to wait several weeks to try again was something called a “solar beta angle cut-out.”

Solar what?

Before sending a shuttle aloft, mission planners carefully calculate the angle defined by its orbital plane around Earth and a line drawn from the center of Earth to the center of the sun. This “solar beta angle” changes constantly as Earth moves around the sun and the shuttle’s orbital plane precesses, or slowly shifts, due to the gravitational tug from Earth’s equatorial bulge.

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